1. Field of the Invention
This invention relates to a method for generating an X-ray with ultrahigh brightness and to an apparatus for generating the same X-ray.
2. Description of the Related Art
In the X-ray diffraction measurement or the like, it is often required that an X-ray with an intensity as high as possible is irradiated onto a sample so as to realize the X-ray diffraction measurement. As such an X-ray generating apparatus as being employed for the X-ray diffraction measurement, an X-ray generating apparatus of rotating anticathode target is conventionally well known.
The rotating anticathode X-ray generating apparatus is configured such that an electron beam is irradiated onto the outer surface of the columnar anticathode target while the columnar anticathode target is rotated under the condition that a cooling medium is flowed in the columnar anticathode target. The rotating anticathode X-ray generating apparatus has an extreme high cooling efficiency because the irradiating portion of the electron beam is varied with time in comparison with an X-ray generating apparatus of stationary target. Therefore, an electron beam can be irradiated onto the anticathode target under the condition of large current to generate an X-ray with high intensity (ultrahigh brightness).
By the way, the output power of an X-ray is generally dependent on an electric power (current×voltage) to be applied between a cathode and an anticathode. On the other hand, since the brightness of the X-ray is defined as (electric power)/(electron beam area on target), the maxi mum electric power is dependent on the electron beam area on a target. Namely, in order to increase the brightness of the X-ray, the electric power is increased while the electron beam area on the target is decreased.
In this case, however, since the intensity of the electron beam is increased per target unit area, the target may be melted and splashed by the electron beam irradiation. Therefore, the brightness of the X-ray can be increased theoretically on the basis of the above-described equation, but can not be increased practically on the basis of the melting point of the target. In this point of view, the brightness of the X-ray is restricted on the melting point of the target.
In this point of view, such an attempt is made in Reference 1 as irradiating an electron beam onto the inner side of the cylindrical portion of the rotating anticathode X-ray generating apparatus so as to heat the irradiating portion to a temperature equal to or near the melting point of the anticathode target. Here, a central axis is set for the rotating anticathode X-ray generating apparatus so that the cylindrical portion can be rotated around the central axis. In this case, since the electron beam irradiating portion is heated to a temperature around the melting point of the anticathode target, the electron beam irradiating portion is at least partially melted. However, since the electron beam irradiating portion is kept against the cylindrical portion by the centrifugal force generated by the rotation of the rotating anticathode target, the partially melted portion, originated from the electron beam irradiation, cannot be splashed outward from the cylindrical portion.
According to Reference 1, therefore, since the intensity of the electron beam to be irradiated onto the rotating anticathode target can be increased per target unit area under the condition that the melting and splashing of the rotating anticathode target are prevented, an X-ray with an relatively higher brightness can be obtained as compared with a conventional one.
[Reference 1] JP-A 2004-172135 (KOKAI)
In view of high resolution analysis, examination and medical application, however, it is required to increase the brightness of the X-ray and thus, develop an X-ray generating method and an X-ray generating apparatus so as to satisfy the above-described requirement.